Electrochemical Reduction of CO 2 to Ethane through Stabilization of an Ethoxy Intermediate

Molecular modification enables CO2 electroreduction to methane on platinum surface in acidic media

Cu-based materials can produce hydrocarbons in CO2 electroreduction (CO2RR), but their stability still needs to be enhanced particularly in acidic media. Metallic Pt is highly stable in both acidic and alkaline media, yet rarely utilized in CO2RR, due to the competitive activity in hydrogen evolution reaction (HER). In this research, abundant thionine (Th) molecules are stably confined within Pt nanocrystals via a molecular doping strategy. The Pt surface is successfully modulated by these Th molecules, and thereby the dominant HER activity is converted to CO2RR activity. CO2 could be electroreduced to CH4 using organic molecule-modified Pt-based catalysts for the first time. Specifically, this composite catalyst maintains more than 100-hour stability in strong acid conditions (pH 1), even comparable to those state-of-the-art CO2RR catalysts. In-situ spectroscopic analysis and theoretical calculations reveal that the molecular modification can decrease the energy barrier for *COOH formation, and guarantee the sufficient local *H near Pt surface. Additionally, the *H derived from H2O dissociation is favorable for the *CO hydrogenation pathway towards *CHO, eventually leading to the formation of CH4. This strategy might be easily applied to microenvironment and interface regulation in other electrocatalytic reactions.

Synergistic Effect of Grain Boundaries and Oxygen Vacancies on Enhanced Selectivity for Electrocatalytic CO2 Reduction

Dual-engineering involved of grain boundaries (GBs) and oxygen vacancies (VO) efficiently engineers the material's catalytic performance by simultaneously introducing favorable electronic and chemical properties. Herein, a novel SnO2 nanoplate is reported with simultaneous oxygen vacancies and abundant grain boundaries (V,G-SnOx/C) for promoting the highly selective conversion of CO2 to value-added formic acid. Attributing to the synergistic effect of employed dual-engineering, the V,G-SnOx/C displays highly catalytic selectivity with a maximum Faradaic efficiency (FE) of 87% for HCOOH production at -1.2 V versus RHE and FEs > 95% for all C1 products (CO and HCOOH) within all applied potential range, outperforming current state-of-the-art electrodes and the amorphous SnOx/C. Theoretical calculations combined with advanced characterizations revealed that GB induces the formation of electron-enriched Sn site, which strengthens the adsorption of *HCOO intermediate. While GBs and VO synergistically lower the reaction energy barrier, thus dramatically enhancing the intrinsic activity and selectivity toward HCOOH.

Positive Valent Metal Sites in Electrochemical CO2 Reduction Reaction

The discovery of high-performance catalysts for the electrochemical CO₂ reduction reaction (CO₂ RR) has faced an enormous challenge for years. The lack of cognition about the surface active structures or centers of catalysts in complex conditions limits the development of advanced catalysts for CO₂ RR. Recently, the positive valent metal sites (PVMS) are demonstrated as a kind of potential active sites, which can facilitate carbon dioxide (CO₂ ) activation and conversation but are always unstable under reduction potentials. Many advanced technologies in theory and experiment have been utilized to understand and develop excellent catalysts with PVMS for CO₂ RR. Here, we present an introduction of some typical catalysts with PVMS in CO₂ RR and give some understanding of the activity and stability for these related catalysts.

A Prospective Life Cycle Assessment of Electrochemical CO2 Reduction to Selective Formic Acid and Ethylene

Converting CO₂ into valuable C₁ -C₂ chemicals through electrochemical CO₂ reduction (ECR) has potential to remedy the ever-increasing climate problems owing to the intensification of industrial activity. In this work, cradle-to-gate life cycle assessment (LCA) was performed to quantify the environmental impacts of formic acid (FA) and ethylene production through ECR benchmarked with the conventional processes. At the midpoint level, global warming potential (GWP) effects of FA and ethylene production through ECR recorded 5.6 and 1.6-times that of the conventional process, respectively. Although ECR currently has limited environmental benefits, the incorporation of hydropower has vast potential after evaluating four sustainable electricity sources, namely hydropower, wind, solar, and biomass. Notably, ECR to FA recorded a 24 % reduction in petrochemical usage. For ethylene production, human health damage, ecosystem damage, and petrochemical use were reduced by 67, 94, and 110 %, respectively. Sensitivity analysis indicated that a sustainable energy supply chain for ECR will accelerate the development of a circular economy.

A stable metal-azolate framework with cyclic tetracopper(I) clusters for highly selective electroreduction of CO2 to C2 products

It is of great significance for constructing electrocatalysts with accurate structures and compositions to pinpoint the active sites, thereby improving the C 2 products (C 2 H 4 , C 2 H 5 OH and CH 3 COOH) selectivity during electrocatalytic CO 2 reduction raction. Here, we report a tetracopper(I) cluster-based metal-organic framework that exhibits long-term stability and remarkable performance for electroreduction CO 2 towards C 2 products in an H-type cell with a maximum Faradaic efficiency (FE) of 72%, and delivers a current density of 350 mA cm -2 with a FE(C 2 ) up to 46% in a flow cell device, outperforming most of the Cu-based electrocatalysts such as Cu derivatives and Cu nanostructured materials. Importantly, no obvious degradation was observed at 350 mA cm -2 over 20 hours of continuous operation, strengthening the practicability. In-situ infrared spectroscopy analysis showed the cooperative effect of adjacent Cu(I) ions in tetracopper(I) cluster may promote the C-C coupling to generate C 2 products.

Roughness Effect of Cu on Electrocatalytic CO2 Reduction towards C2H4

Electrochemical reduction of CO 2 to produce valuable multi-carbon products is a promising avenue for promoting CO 2 conversion and achieving renewable energy storage, and it has also attracted considerable attention recently. However, the synthesis of Cu electrode with a controllable electrochemical active surface area (ECSA) to understand its role in CO 2 reduction to C 2 H 4 remains challenging. Herein, a series of Cu electrodes with different ECSA is synthesized through a simple oxidation-reduction approach. We reveal that the improved selectivity of C 2 H 4 is proportional to the ECSA of Cu in the low ECSA range, and a further increase in ECSA has a negligible effect on its selectivity. The enlarged surface area could strengthen the local pH effect near the surface of Cu electrode and suppress the generation of C 1 products as well as H 2 . The study provides a feasible strategy to rationally design electrocatalysts with high electrochemical CO 2 reduction performances.

Oxide Derived Copper for Electrochemical Reduction of CO2 to C2+ Products

The electrochemical reduction of carbon dioxide (CO₂) on copper electrode derived from cupric oxide (CuO), named oxide derived copper (ODCu), was studied thoroughly in the potential range of −1.0 V to −1.5 V versus RHE. The CuO nanoparticles were prepared by the hydrothermal method. The ODCu electrode was used for carbon dioxide reduction and the results revealed that this electrode is highly selective for C₂₊ products with enhanced current density at significantly less overpotential. This catalyst shifts the selectivity towards C₂₊ products with the highest Faradaic efficiency up to 58% at −0.95 V. In addition, C₂ product formation at the lowest onset potential of −0.1 V is achieved with the proposed catalyst. X-ray diffraction and scanning electron microscopy revealed the reduction of CuO to Cu (111) nanoparticles during the CO₂ RR. The intrinsic property of the synthesized catalyst and its surface reduction are suggested to induce sites or edges for facilitating the dimerization and coupling of intermediates to ethanol and ethylene.

Photocatalytic CO2 Reduction Using TiO2-Based Photocatalysts and TiO2 Z-Scheme Heterojunction Composites: A Review

Photocatalytic CO₂ reduction is a most promising technique to capture CO₂ and reduce it to non-fossil fuel and other valuable compounds. Today, we are facing serious environmental issues due to the usage of excessive amounts of non-renewable energy resources. In this aspect, photocatalytic CO₂ reduction will provide us with energy-enriched compounds and help to keep our environment clean and healthy. For this purpose, various photocatalysts have been designed to obtain selective products and improve efficiency of the system. Semiconductor materials have received great attention and have showed good performances for CO₂ reduction. Titanium dioxide has been widely explored as a photocatalyst for CO₂ reduction among the semiconductors due to its suitable electronic/optical properties, availability at low cost, thermal stability, low toxicity, and high photoactivity. Inspired by natural photosynthesis, the artificial Z-scheme of photocatalyst is constructed to provide an easy method to enhance efficiency of CO₂ reduction. This review covers literature in this field, particularly the studies about the photocatalytic system, TiO₂ Z-scheme heterojunction composites, and use of transition metals for CO₂ photoreduction. Lastly, challenges and opportunities are described to open a new era in engineering and attain good performances with semiconductor materials for photocatalytic CO₂ reduction.

Local Environment Determined Reactant Adsorption Configuration for Enhanced Electrocatalytic Acetone Hydrogenation to Propane

We demonstrate a widely applicable method to alter the adsorption configuration of multi-carbon containing reactants by no catalyst engineering but simply adjusting the local reaction environment of the catalyst surface. Using electrocatalytic acetone to propane hydrogenation (APH) as a model reaction and common commercial Pt/Pt-based materials as catalysts, we found local H⁺ concentration can significantly influence the adsorption mode of acetone reactant, for example, in vertical or flat mode, and target product selectivity. Electrocatalytic measurement combined with in situ spectroscopic characterizations reveals that the vertically adsorbed acetone is favorable for propane production while the flatly adsorbed mode suppresses the reaction. DFT calculations indicate that the H coverage on catalyst surface plays a decisive role in the adsorption configuration of acetone. The increased local acidity can facilitate the adsorption configuration of acetone from flat to vertical mode and suppress the competing hydrogen evaluation reaction, which consequently enhances the APH selectivity.

The Controllable Reconstruction of Bi-MOFs for Electrochemical CO2 Reduction through Electrolyte and Potential Mediation

Monitoring and controlling the reconstruction of materials under working conditions is crucial for the precise identification of active sites, elucidation of reaction mechanisms, and rational design of advanced catalysts. Herein, a Bi-based metal-organic framework (Bi-MOF) for electrochemical CO₂ reduction is selected as a case study. In situ Raman spectra combined with ex situ electron microscopy reveal that the intricate reconstruction of the Bi-MOF can be controlled using two steps: 1) electrolyte-mediated dissociation and conversion of Bi-MOF to Bi₂ O₂ CO₃ , and 2) potential-mediated reduction of Bi₂ O₂ CO₃ to Bi. The intentionally reconstructed Bi catalyst exhibits excellent activity, selectivity, and durability for formate production, and the unsaturated surface Bi atoms formed during reconstruction become the active sites. This work emphasizes the significant impact of pre-catalyst reconstruction under working conditions and provides insight into the design of highly active and stable electrocatalysts through the regulation of these processes.

High-Rate CO2 Electroreduction to C2+ Products over a Copper-Copper Iodide Catalyst

Electrochemical CO₂ reduction reaction (CO₂ RR) to multicarbon hydrocarbon and oxygenate (C₂₊ ) products with high energy density and wide availability is of great importance, as it provides a promising way to achieve the renewable energy storage and close the carbon cycle. Herein we design a Cu-CuI composite catalyst with abundant Cu⁰ /Cu⁺ interfaces by physically mixing Cu nanoparticles and CuI powders. The composite catalyst achieves a remarkable C₂₊ partial current density of 591 mA cm^-2 at -1.0 V vs. reversible hydrogen electrode in a flow cell, substantially higher than Cu (329 mA cm^-2 ) and CuI (96 mA cm^-2 ) counterparts. Induced by alkaline electrolyte and applied potential, the Cu-CuI composite catalyst undergoes significant reconstruction under CO₂ RR conditions. The high-rate C₂₊ production over Cu-CuI is ascribed to the presence of residual Cu⁺ and adsorbed iodine species which improve CO adsorption and facilitate C-C coupling.

Residual Chlorine Induced Cationic Active Species on a Porous Copper Electrocatalyst for Highly Stable Electrochemical CO2 Reduction to C2

Electrochemical carbon dioxide (CO₂ ) reduction reaction (CO₂ RR) is an attractive approach to deal with the emission of CO₂ and to produce valuable fuels and chemicals in a carbon-neutral way. Many efforts have been devoted to boost the activity and selectivity of high-value multicarbon products (C₂₊ ) on Cu-based electrocatalysts. However, Cu-based CO₂ RR electrocatalysts suffer from poor catalytic stability mainly due to the structural degradation and loss of active species under CO₂ RR condition. To date, most reported Cu-based electrocatalysts present stabilities over dozens of hours, which limits the advance of Cu-based electrocatalysts for CO₂ RR. Herein, a porous chlorine-doped Cu electrocatalyst exhibits high C₂₊ Faradaic efficiency (FE) of 53.8 % at -1.00 V versus reversible hydrogen electrode (V_RHE ). Importantly, the catalyst exhibited an outstanding catalytic stability in long-term electrocatalysis over 240 h. Experimental results show that the chlorine-induced stable cationic Cu⁰ /Cu⁺ species and the well-preserved structure with abundant active sites are critical to the high FE of C₂₊ in the long-term run of electrochemical CO₂ reduction.

Grain-Boundary-Engineered La2CuO4 Perovskite Nanobamboos for Efficient CO2 Reduction Reaction

Electroreduction of carbon dioxide (CO₂RR) has been regarded as a promising approach to realize the production of useful fuels and to decrease greenhouse gas levels simultaneously, where high-efficiency catalysts are required. Herein, we report La₂CuO₄ nanobamboo (La₂CuO₄ NBs) perovskite with rich twin boundaries showing a high Faraday efficiency (FE) of 60% toward ethylene (C₂H₄), whereas bulk La₂CuO₄ exhibits a FE_CO of 91%. X-ray absorption spectroscopy (XAS) reveals that the Cu in La₂CuO₄ NBs is in the Cu²⁺ state, and no obvious change can be observed during the catalytic process, as monitored by in situ XAS. Density functional theory calculations reveal that the superior FE_C2H4 of La₂CuO₄ NBs originates from the active (113) surfaces with intrinsic strain. The formation of gap states annihilates the electron transfer barrier of C-C coupling, resulting in the high FE_C2H4. This work provides a new perspective for developing efficient perovskite catalysts via grain boundary engineering.